The present invention relates to a device for driving a photoconductive element which is installed in an electrophotographic copier, particularly a color electrophotographic copier, and to a mechanism for supporting the photoconductive element.
Today, there is extensively used an electrophotographic copier in which a transfer roller is pressed against a photoconductive drum to transfer from the drum to a paper sheet a toner image which has been produced on the drum by developing an electrostatic latent image, especially a color electrophotographic copier which repeats such image transfer a certain number of times corresponding to the number of colors separated. Specifically, in a color electrophotographic copier, a photoconductive drum and a transfer drum are each rotated a predetermined number of times which is equal to the number of colors separated. This allows toner images sequentially formed on a photoconductive drum and each associated with a different color to be transferred one upon another on a paper sheet, thereby reproducing a predetermined color image. To insure register of the colors, a gear is mounted on one end of each of the two drums, and these two gears are held in mesh with each other. A drive motor mounted in a body of the copier to serve as a drive source is operatively connected to one of the gears by a transmission mechanism which includes a timing belt, whereby the rotations of the two drums are synchronized to each other.
A drawback with such an intermeshing gear scheme is that backlash is apt to occur between the two gears to invite vibrations of the drums, causing the toner images of different colors to be out of register with each other. Another drawback is that, since a plurality of transmitting means which include a timing belt are used, the arrangement is complicated, the torque is apt to fluctuate, the durability is limited, and, therefore, quality image reproduction is not attainable.
In the light of this, there has been proposed a drive system in which an outer rotor type drive motor or the like is mounted in each of the photoconductive and transfer drums. This type of system, however, has both advantages and disadvantages. Specifically, one advantage is that, since the drive sources associated with the drums are independent of each other, the color-by-color operation does not have to be associated with one rotation of the photoconductive drum and, hence, the period of time necessary for copying is reduced. A disadvantage is that the driving devices which are built in the drums cannot be maintained, assembled or adjusted without time- and labor-consuming work. Another disadvantage is that the outer rotor type motor has to be rigidly supported to prevent its vibrations due to rotation from affecting the copier body, resulting in an increase in cost.